Final answer:
A deficiency of thiamine, essential for carbohydrate metabolism and neural function, is a key nutritional problem contributing to substance-induced persisting dementia from long-term alcohol use.
Step-by-step explanation:
A nurse planning care for a client with substance-induced persisting dementia due to long-term alcohol use should be aware that the nutritional problem contributing to this condition, aside from the direct effects of alcohol on brain tissue, is a deficiency of thiamine. Thiamine, also known as vitamin B1, plays a critical role in carbohydrate metabolism and neural function. Long-term alcohol consumption can lead to a reduction in thiamine absorption and storage, which, if inadequately treated, can result in Wernicke's encephalopathy and eventually lead to persisting dementia. Thiamine deficiency manifests in the body through loss of appetite, cardiac problems, edema, muscular atrophy, and various neurological impairments such as polyneuritis, highlighting its vital importance for brain health.